The present invention relates to (i) a light-diffusing agent for use in, for example, a mold article having light-diffusing properties such as a light-diffusing film and a light-diffusing panel for a backlight or illuminating device of a liquid crystal display, (ii) a grain aggregate which can preferably be adopted as various surf ace treatment agents such as a matte agent and a coating material, a catalyst carrier, an additive of a resin molded material and the like, and (iii) a producing method of the grain aggregate.
A grain aggregate is widely used in a coating material, various surface treatment agents, a catalyst carrier, an additive of a resin mold material and others. What has been highly called for in recent years is a grain aggregate of cross-linking polymeric grains having higher heat resistance, higher strength, and higher solvent resistance. The grain aggregate can be produced by, for example, a method disclosed in the Publication of Japanese Patent No. 2559833 (Date of patent: Sep. 5, 1996). According to this publication, grains are fused by adding a solvent after aggregating a polymer latex. However, this method employs an organic solvent, thereby requiring processing of the organic solvent. Further, when producing the grain aggregate of the cross-linking polymeric grains by this method, there arises such a problem that the fusion of the cross-linking polymeric grains can hardly occur by an application of heat, thereby preventing an easy formation of an aggregate.
The grain aggregate of the cross-linking polymeric grains can be produced by, for example, a method disclosed in Japanese Unexamined Patent Publication No. 70741/1990 (Tokukaihei 2-70741 published on Mar. 9, 1990). In this publication, a polymer including a carboxylic unsaturated acid is neutrally swollen so that it can be used as a seed grain, and as a second step, an emulsion-polymerization of a polymer having a composition different from that of the polymer of the seed grain is carried out so as to obtain a grain aggregate of the cross-linking polymeric grains.
However, by this method, in the emulsion-polymerization at the second step, a condition to avoid generation of a new grain should be selected. Thus, there arises a problem of limitation in composition of a polymer and/or a polymerization condition. A further problem is that the resultant grain aggregate is poor in strength and easily destroyed.
As explained, neither methods for easily producing a grain aggregate of the cross-linking polymeric grains nor a grain aggregate with the high strength have conventionally been known.
Further, the inventors of the present invention have formerly discovered that a cross-linking polymeric grain can efficiently be obtained by adopting a spray drying method to dry cross-linking polymeric grains obtained from polymerization of a mixture of vinyl-family monomers including monomers having cross-linking characteristics such as divinylbenzene and trimethylolpropane tri(meth)acrylate (Japanese Unexamined Patent Publication No. 53720/2000 [Tokukai 2000-53720 published on Feb. 22, 2000]). By this method can be obtained such a grain aggregate that has high heat resistance and high strength, maintains the shape of a cross-linking polymeric grain, and has a large specific surface area. However, recently, a demand for a further improvement in the heat resistance and the solvent resistance of the grain aggregate has been increasing.
Meanwhile, conventionally, a variety of liquid crystal display devices have been adopting a backlight to project light from a rear side of a liquid crystal. Particularly, devices such as a laptop PC which has been required to further reduce a volume and a size adopts a method for propagating light by means of a sidelit surface light source device so that the light is uniformly diffused by a light-diffusing film and the like. The light-diffusing film is commonly produced by a method for coating a surface of a transparent film which is a base material with a mixture of inorganic or organic grains and binders. Further, a light-diffusing panel is produced by a method for coating a surface of a transparent panel of glass, plastic or like with a mixture of inorganic or organic grains and binders, or a method for molding the panel by blending a resin such as a polyester resin or epoxy resin with grains.
However, the conventional light-diffusing film and light-diffusing panel have a problem such that a distribution of brightness fluctuates in accordance with a difference in angle with respect to a light projecting surface. Therefore, an improvement has been made to propagate the light by uniformly diffusing it while enhancing light transmissivity. More specifically, methods for such an improvement includes, for example, a method adopting a grain made of an organic substance, which is completely spherical in shape, for improving a ratio of grains to binders when blending the grains and the binders so as to coat the surface of the film or panel (Japanese Unexamined Patent Publication No. 35124/1993 [Tokukaihei 5-35124 published on Feb. 12, 1993]; Japanese Unexamined Patent Publication No. 16732/1996 [Tokukaihei 8-16732 published on Jan. 19, 1996]), a method for improving the shape of a surface to be coated (Japanese Unexamined Patent Publication No. 118830/1996 [Tokukaihei 8-118830 published on May 14, 1996]; Japanese Unexamined Patent Publication No. 121878/1996 [Tokukaihei 8-121878 published on May 17, 1996]), and a method for improving a burial state of grains under a surface to be coated (Japanese Unexamined Patent Publication No. 229202/1997 [Tokukaihei 9-229202 published on Sep. 5, 1997]), where particularly a coating method has been examined in various forms. A method for improving a grain itself, however, has not been taken into consideration. Accordingly, a current problem of the light-diffusing film and the light-diffusing panel is that they have not attained a sufficient distribution of brightness and light transmissivity.
It is a first object of the present invention to provide a grain aggregate having higher heat resistance, higher solvent resistance, higher strength, higher light-diffusing properties, and a large specified surface area, and a method for readily producing the grain aggregate.
In order to attain the foregoing object, the grain aggregate according to the present invention is made up of a plurality of cross-linking polymeric grains bonding together via a substance having a reactive functional group.
With this arrangement, a grain aggregate having strong bonding among the cross-linking polymeric grains can be obtained, thereby making it possible to provide a grain aggregate having the greatly improved heat resistance, solvent resistance, strength and light-diffusing properties, and the large specific surface area.
Further, in order to attain the foregoing object, the grain aggregate according to the present invention is made up of a plurality of differently composed grains of at least two types bonding together.
With this arrangement, a grain aggregate provided with the respective properties of the plurality of the differently composed grains bonding together can be obtained, thereby making it possible to provide a grain aggregate having the further improved heat resistance, solvent resistance, strength and light-diffusing properties. In addition, the grain aggregate is effective when used in, for example, various surface treatment agents such as a coating material, a matte agent and a light-diffusing agent, a catalyst carrier, an additive of a resin mold material, and others.
In order to attain the foregoing object, a producing method of the grain aggregate according to the present invention includes the step of drying by spraying a dispersion liquid containing the cross-linking polymeric grains and a substance having a reactive functional group.
The spraying is performed under no particularly limited conditions, insofar as the shape and drying condition of the obtained grain aggregate are not adversely affected. More specifically, for example, depending on a shape of a nozzle used in the spraying, the dispersion liquid containing the cross-linking polymeric grains and the substance having a reactive functional group may separately be dried by spraying with different nozzles. Most preferable is the spray drying of a blend liquid of the dispersion liquid containing the cross-linking polymeric grains and the substance having a reactive functional group.
With this arrangement, by the spray drying of the blend liquid of the dispersion liquid containing the cross-linking polymeric grains and the substance having the reactive functional group, there can be formed a grain aggregate in which the plurality of cross-linking polymeric grains more efficiently bond together via the substance having a reactive functional group, thereby making it possible to further improve heat resistance, solvent resistance, strength and light-diffusing properties. In addition, by the spray drying can readily be obtained a grain aggregate while maintaining the individual shape of the cross-linking polymeric grain before the formation of the grain aggregate, thereby readily producing a grain aggregate having a large specific surface area.
Further, in order to attain the foregoing object, the producing method of the grain aggregate according to the present invention includes the step of drying by spraying at least two different types of dispersion liquids each containing a plurality of grains. More preferably, in order to attain the foregoing object, the producing method of the grain aggregate according to the present invention includes the step of drying by spraying a dispersion liquid which is containing at least two different types of a plurality of grains.
In addition, the producing method of the grain aggregate according to the present invention also includes the step of drying by spraying a dispersion liquid containing the plurality of grains and a substance having a reactive functional group. For example, the plurality of grains may be made of either an organic substance or an inorganic substance. More specifically, by allowing grains made of an organic substance, such as differently composed cross-linking polymeric grains and/or cross-linking resin grains, and/or grains made of an inorganic substance which is silica and the like to bond together via a substance having a reactive functional group, a grain aggregate having a combination of different properties can be attained, thereby easily producing a grain aggregate having the further improved heat resistance, solvent resistance, strength and light-diffusing properties. Further, it is more preferable that each of the plurality of grains may at least be a grain selected from the group consisting of a cross-linking polymeric grain, a cross-linking resin grain and an inorganic grain. More preferably, the plurality of grains essentially consist of an organic substance. Alternatively, it is more preferable that the plurality of grains essentially consist of an organic substance and an inorganic substance.
It is a second object of the present invention to provide a light-diffusing agent containing the grain aggregate and having high transmissivity and sufficient light-diffusing properties, and a light-diffusing mold article containing the light-diffusing agent, such as a light-diffusing film and a light-diffusing panel. Further, a third object of the present invention is to provide a liquid crystal panel adopting the light-diffusing film.
In order to attain the foregoing object, the light-diffusing agent according to the present invention includes a grain aggregate in which a plurality of cross-linking polymeric grains bond together.
Further, in order to attain the foregoing object, the light-diffusing agent according to the present invention includes at least two different types of grain aggregates respectively made up of a plurality of grains bonding together.
With this arrangement, the light-diffusing agent has superior light-diffusing properties and light transmissivity per grain aggregate while being light in weight, thereby requiring a smaller amount of addition so as to be highly effective than a conventional light-diffusing agent.
The light-diffusing mold article according to the present invention includes the light-diffusing agent.
With this arrangement, by thus including the grain aggregate having the improved light-diffusing properties, it is possible to provide the light-diffusing agent and light-diffusing mold article both having the further improved light-diffusing properties. In addition, in the case where the light-diffusing agent of the present invention is used to produce a light-diffusing mold article which is then applied to a backlight and the like of a liquid crystal display device, high brightness and a wide angle of visibility can be attained.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.